This invention relates to the preparation of cyclic ethers such as tetrahydrofuran, furan, tetrahydropyran, 1,4-dioxane, and the like, and more particularly, to the preparation of such cyclic ethers by the catalytic cyclodehydration of a suitable organic starting material possessing at least two hydroxyl groups.
Processes for the cyclodehydration of glycols and glycol ethers to provide cyclic ethers are known.
U.S. Pat. No. 2,251,835 describes the cyclodehydration of 1,4-butanediol in the presence of alumina and phosphoric acid catalysts to provide the commercially important cyclic ether tetrahydrofuran. The process described in U.S. Pat. No. 4,007,095 provides 1,4-dioxane, another commercially important cyclic ether, from the cyclodehydration of ethylene glycol or a polyethylene glycol employing an acid catalyst such as sulfuric acid. According to U.S. Pat. No. 4,093,633, tetrahydrofuran is obtained by cyclodehydrating 1,4-butanediol in the presence of an acid catalyst such as sulfuric acid, the product ether being separated from by-product water in a triple column distillation unit. U.S. Pat. No. 4,136,099 discloses the use of tungsten oxide to catalyze the cyclodehydration of 1,4-butanediol to tetrahydrofuran. U.S. Pat. No. 4,196,130 describes he dehydration of diols to cyclic ethers employing aluminum oxide catalyst. U.S. Pat. No. 4,203,908 discloses the dehydration of diols in the liquid phase in the presence of a bleaching earth as the catalyst and of a minor amount of an alkali metal or alkaline earth metal carbonate or bicarbonate. Inoue, et al., Bull. Chem. Soc. Jpn., 53, 3031-3032 (1980) describes the preparation of a variety of saturated and unsaturated cyclic ethers including tetrahydrofuran, tetrahydropyran, tetrahydropyran 2-methanol, 1,4-dioxane, etc., by dehydrating glycol and triol compounds in the presence of an alumina catalyst. Khai, et al., J. Org. Chem., 46, 1759-1760 (1981) describes the cyclization of alpha, omega aliphatic diamines to heterocyclic amines and ammonia employing dichlorotris (triphenylphosphine) ruthenium (II) catalyst complex. No mention is made in this publication of the cyclodehydration of polyhydroxy compounds.